As human beings our perception of risk is shaky and often runs counter to the actual real risks and expected values. Phenomena such as the recency effect, in which more recent events are often given greater weighting by people for things such as risk, distort decisions, actions and public policy.

An example is the relatively unknown risk posed by radon gas as compared to the hue and cry over water bottles made from bisphenol-A. Even normally rational Black Belts often forget their training and fall prey to uncritical weighing of risks as reported by a 30-second news item. Radon gas is the second highest cause of lung cancer after smoking, yet when was the last time you heard about it? As Tom Blackwell posted last week in an article for The National Post:

Radon seeping invisibly into some Canadian homes causes hundreds more lung-cancer deaths a year than previously thought, a Health Canada study based on a recent testing blitz has concluded.

The department has almost doubled the estimated risk posed by the radioactive gas, saying it likely accounts for 16% of lung cancer cases, up from the 10% estimate that had been accepted for decades.

About 3,200 Canadians a year likely die because of exposure to radon, produced naturally when uranium in the soil degrades, say the study authors. Efforts to reduce radon levels need to be stepped up, they urge in a paper appearing in the journal Radiation Protection Dosimetry.

Health Canada is working hard to raise awareness, but it is an “uphill battle,” said Kelly Bush, the department’s spokeswoman on the issue.

People sometimes respond strongly to relatively minor risks posed by man-made substances, while all but ignoring the much more significant, yet natural threat of radon, she said.

“I think they need to take it very seriously,” said Ms. Bush. “It’s much more significant than a lot of other environmental health risks that people react to, for example [plastics ingredient] bisphenol-A and throwing out all the plastic baby bottles, when the risk is quite a bit smaller than radon,” she said.

“The problem is that that risk is tangible and you can blame someone: the people who made those bottles. With radon, you can’t blame anyone, because it’s naturally occurring. You can’t smell it, see it or taste it. And it’s not immediate, it’s long term.” Ms. Bush said she has no problem grasping the human aspect of the problem, however, given that she frequently hears from people who have been directly affected.

“I get the calls from the 40 or 50-year-old Canadians with lung cancer who have never smoked and say, ‘I wish I had known’ or ‘I wish I had tested.’ And that’s what keeps me going.” She recommended that Canadians everywhere test their homes for radon levels, either with do-it-yourself kits sold at hardware stores or by hiring professionals, and take corrective action if needed.

Homes in Manitoba, Saskatchewan and New Brunswick are more likely than others to have high levels.

The study has produced some “important findings,” more accurately defining the scope of a problem that is overlooked by many Canadians, said Prithwish De, an epidemiologist at the Canadian Cancer Society.

“It gives us more reason to push for radon testing,” he said.

Radon is produced by the decay of uranium in rocks and soil throughout the Earth’s crust. In the enclosed spaces of a house, it can accumulate to levels that are dangerous for people exposed to the gas over long periods.

Though most of the 25,000 new lung cancer cases and 20,000 lung-cancer deaths a year result from smoking, radon is the next biggest cause of the most deadly type of malignancy. The previous estimate of radon’s role in the disease was based on testing of homes conducted in the 1970s.

The just-published study on cancer risk stemmed from a new radon survey of 14,000 residences carried out by Health Canada from 2009 to 2011, using techniques designed to capture a more exact picture of the phenomenon.

Officials found that 7% of houses nationally have levels of radon above 200 becquerels per cubic metre of air (Bqm³) – considered the point where corrective action should be taken – up from 3% to 5% in the older survey.

The risk seems much more widespread in certain provinces, with one in five Manitoba and New Brunswick homes, for instance, registering above the limit.

The recent study by Jing Chen and other scientists at Health Canada’s radiation protection bureau used those new radon figures – and recognized formulas for translating radiation exposure into cancer risk – to estimate the percentage of the country’s lung cancer cases triggered by radon.

The estimate of radon-linked deaths climbed to 3,200 annually from about 2,000. By comparison, it is estimated that exposure to asbestos triggers 1,500 new cancer cases a year in Canada.

Ms. Bush said testing can be done for as little as $50 using a home kit. If radon levels are above 200 Bqm³, the most effective way to fix the problem is so-called “active soil depressurization,” where a pipe is installed into the earth below the foundation, then fed outside the house, a method that draws over 90% of contaminated air away from the home. The cost is $1,000 to $3,000, she said.